Hi,@Vikram Midha
For example, we set Deadline to 10 days from now at 8PM, I test the script in my lab, it create the deployment well:
[datetime]$DeadlineTime = (get-date -Hour 20 -Minute 0 -Second 0).AddDays(10)
$NewScheduleDeadline = New-CMSchedule -Start $DeadlineTime -Nonrecurring
New-CMPackageDeployment -CollectionName "collection name here" -PackageName "package name here" -StandardProgramName "package program name" -DeployPurpose required -AvailableDateTime "2020-12-10 13:00" -StandardProgram -FastNetworkOption DownloadContentFromDistributionPointAndRunLocally -SlowNetworkOption DownloadContentFromDistributionPointAndLocally -RerunBehavior RerunIfFailedPreviousAttempt -Schedule $NewScheduleDeadline